docs: def sort(self):
          """Sort the data so that x is monotonically increasing and contains
          no duplicates.
          """
          if 'wavelength' in self.rsr:
              # Only one detector apparently:
              self.rsr['wavelength'], self.rsr['response'] = \
                  sort_data(self.rsr['wavelength'], self.rsr['response'])
          else:
              for detector_name in self.rsr:
                  (self.rsr[detector_name]['wavelength'],
                   self.rsr[detector_name]['response']) = \
                      sort_data(self.rsr[detector_name]['wavelength'],
                                self.rsr[detector_name]['response'])